Goat head weed (Tribulus terrestris), also called puncturevine, is a summer annual plant known for its sharp, tack-like seed burrs. This fast-growing weed quickly colonizes disturbed areas, roadsides, and lawns, creating a painful hazard for people, pets, and bicycle tires. Due to its aggressive life cycle and prolific seed production, eradication requires persistence and a combination of control methods.
Identifying Goat Head Weeds and Understanding Their Life Cycle
Goat head weed is a prostrate, mat-forming plant that grows low to the ground. Stems radiate outward from a central taproot, forming patches up to five feet in diameter. The leaves are small and hairy, divided into four to eight pairs of smaller leaflets. Small, bright yellow flowers with five petals appear from spring through fall in warm climates.
The plant’s defining feature is its fruit: a hard, spiny burr that breaks into five sharp, woody sections, each containing up to four seeds. A single plant can produce thousands of seeds per season. These seeds remain viable and dormant in the soil for three to seven years, creating a substantial seed bank. As a summer annual, the plant germinates when temperatures warm in the spring and grows until the first frost, making control efforts before burr production essential.
Non-Chemical Eradication Methods
For small infestations, manual and mechanical removal offers an immediate solution, though it requires consistent effort. Hand-pulling is the most effective non-chemical method and is easiest when the soil is moist. It is important to remove the entire taproot to prevent regrowth; thick gloves should be worn to protect hands from the sharp burrs.
If burrs have already been produced, the entire plant must be carefully bagged and disposed of without dropping seeds on the ground. Mechanical methods like hoeing or tilling can sever the taproot beneath the soil surface. However, tilling may bring dormant seeds closer to the surface, potentially causing new germination.
Solarization is a cultural control technique that uses clear plastic sheeting to trap solar energy, raising the soil temperature high enough to kill seeds and existing plants. This involves covering the infested area with plastic for several weeks during the hottest part of the summer. Smothering the area with a thick layer of organic mulch or old carpet also blocks sunlight and prevents germination.
Effective Herbicide Strategies
Chemical control is often necessary for large infestations and relies on using the right herbicide at the correct stage of the plant’s life cycle. The strategy uses pre-emergent and post-emergent applications.
Pre-Emergent Control
Pre-emergent herbicides are applied in late winter or early spring before the seeds germinate, targeting the seeds in the soil. Active ingredients like pendimethalin, trifluralin, or oryzalin create a chemical barrier that stops seedlings from establishing. This long-term control measure must be reapplied annually to deplete the seed bank.
Post-Emergent Control
Once goat head plants have emerged and are actively growing, post-emergent herbicides are needed. These are most effective when applied to young plants, ideally before the spiny burrs have hardened. Common selective herbicides for broadleaf weeds, which will not harm desirable turfgrass, contain active ingredients such as 2,4-D, dicamba, or triclopyr. For non-turf areas, a non-selective herbicide containing glyphosate can be used as a spot treatment. Note that herbicides containing 2,4-D or dicamba can injure other desirable broadleaf plants.
Long-Term Prevention and Cleanup
Managing the existing seed bank and preventing the spread of new burrs is the most challenging aspect of control. After pulling or chemically treating plants, proper disposal is critical to prevent re-infestation.
All plant material, especially those with mature burrs, must be sealed in heavy-duty garbage bags and sent to a landfill. They should never be added to a compost pile, as the seeds will survive the composting process.
Preventing new establishment involves creating an environment where the weed cannot thrive. Since goat heads prefer bare, disturbed soil, establishing a dense, competitive groundcover like healthy turfgrass or other desirable plants significantly reduces germination. Regular maintenance, such as using a thick layer of mulch in garden beds, will block sunlight and suppress germination.
Routine inspection and cleaning are necessary to stop the spread of burrs. Burrs easily cling to shoe treads, vehicle tires, and pet fur, acting as transportation devices. Cleaning these items thoroughly after being in an infested area prevents inadvertently planting the weed elsewhere.